Beginning Python - From Novice to Professional

CHAPTER 11 ■ FILES AND STUFF 267
>>> third
'This is the third line\n'
■Note The syntax print >> file, text prints the text to the given file object.
In this example, it’s important to note the following:
• I’ve used print to write to the file; this automatically adds newlines after the strings
I supply.
• I use sequence unpacking on the opened file, putting each line in a separate variable.
(This isn’t exactly common practice because you usually won’t know the number of lines
in your file, but it demonstrates the “iteratorness” of the file object.)
• I close the file after having written to it, to ensure that the data is flushed to disk. (As you
can see, I haven’t closed it after reading from it. Sloppy, perhaps, but not critical.)
A Quick Summary
In this chapter, you’ve seen how to interact with the environment through files and file-like
objects, one of the most important techniques for I/O (input/output) in Python. Here are some
of the highlights from the chapter:
File-like objects. A file-like object is (informally) an object that supports a set of methods
such as read and readline (and possibly write and writelines).
Opening and closing files. You open a file with the open function (in newer versions of
Python, actually just an alias for file), by supplying a file name.
Modes and file types. When opening a file, you can also supply a mode, such as 'r' for read
mode or 'w' for write mode. By appending 'b' to your mode, you can open files as binary
files. (This is necessary only on platforms where Python performs line-ending conversion,
such as Windows.)
Standard streams. The three standard files (stdin, stdout, and stderr, found in the sys
module) are file-like objects that implement the UNIX standard I/O mechanism (also
available in Windows).
Reading and writing. You read from a file or file-like object using the method read. You
write with the method write.
Reading and writing lines. You can read lines from a file using readline, readlines, and
(for efficient iteration) xreadlines. You can write files with writelines.
Iterating over file contents. There are many ways of iterating over file contents. It is most
common to iterate over the lines of a text file, and you can do this by simply iterating over
the file itself. There are other methods too, such as readlines and xreadlines, that are
compatible with older versions of Python.